In a conventional domestic toilet, only one valve controls the refilling functions of both the tank and the toilet bowl after flushing. One tube refills the tank, and a second tube refills the toilet bowl. When open, the valve supplies water to both tubes simultaneously. Water only ceases to flow when the tank becomes full of water, lifting a float ball to shut off the valve.
Should the tank become too full, it spills into an overflow tube which directs water to the toilet bowl. The bowl refill tube discharges water into the overflow tube so that, in the normal course of events, water is also directed to the toilet bowl.
The bowl has a water trap at its base, which seals against the escape of sewer gas and establishes a maximum water level in the bowl before overflowing to the sewer. If the bowl refills to its maximum level before the tank is full then the valve continues to supply excess water to the bowl which overflows and is wasted as it is lost down the sewer.
In conventional domestic toilets the bowl refill tube typically fills the bowl before the tank refill tube fills the tank. By ensuring the bowl fills first one can be assured of a water seal and the bowl is maintained in its cleanest state. Unfortunately, this results in wasted water.
Toilets from, different manufacturers and even similar toilets have individual refill characteristics. Use of a flow-restriction device which has one or even several possible flows is inadequate to balance bowl and tank fill rates across a range of different toilets.
In U.S. Pat. No. 5,134,729 to Shaw, one or more flow nozzles or conduits are inserted within the termination of the bore of the bowl refill tube. If the original flow rate of water to the bowl is too great, then a conduit having a smaller diameter bore than that of the refill tube is inserted. If the flow is still too great, then a second smaller conduit is inserted within the bore of the first conduit. Each conduit causes a step reduction in the flow rate. This method is severely limited by the availability of suitably sized conduits. Further, the number of subsequent incremental insertions is limited by the cumulative wall thickness of the conduits. Shaw only contemplates two incremental restrictions to the flow.
In U.S. Pat. No. 5,287,565 to Auman et al., like Shaw, a device is installed at the termination of the bowl refill tube. The device comprises a chamber having a linear array of identically sized discharge tubes. The device is attached to the overflow tube. The discharge tubes divide the bowl refill flow between either the overflow tube or the tank. The bowl refill rate is adjusted by selecting how many of the discharge tubes direct their flow to the overflow tube (and thus the bowl) and by difference, how many direct their flow to the tank. The balance between bowl and tank flow is limited to a finite number of steps, defined by the number of discharge tubes and the space provided by the overflow tube.
Due to the variability of toilet bowl fill rates, even among identical toilet models, the prior art devices are not able to ensure proper balance between tank and bowl refill rates, resulting in continued waste of water in many cases.